Embodiments of the invention relate generally to electronic power conversion and, more particularly, to a dual-input inverter topology and method of controlling thereof that allows for the output of two DC sources to be combined in the same inverter.
Photovoltaic (PV) power systems are power systems that employ a plurality of solar modules to convert sunlight into electricity. PV systems include multiple components, including photovoltaic modules, mechanical and electrical connections and mountings, and means of regulating or modifying the electrical output. One common arrangement in PV systems is for several PV modules to be connected in series to form a PV string, with multiple PV strings in a PV system then being combined in parallel to aggregate the current in a PV array. Photovoltaic (PV) cells generate direct current (DC) power, with the level of DC current being dependent on solar irradiation and the level of DC voltage dependent on temperature. When alternating current (AC) power is desired, an inverter is used to convert the DC energy into AC energy, such as AC energy suitable for transfer to a power grid.
For converting the varying DC voltage of a PV array to the fixed frequency AC voltage of the power grid, PV inverters may employ either a single-stage conversion power circuit in which a transformer is employed to boost the AC voltage or a two-stage conversion power circuit that uses a DC link as an intermediate energy storage step, which means that the converter first converts the unstable PV array voltage to a stable DC voltage. The PV inverter then subsequently converts the stable voltage into an AC current that can be injected into the grid. In a two-stage PV inverter, often the first stage includes a boost converter, and the second stage includes a single-phase or three-phase inverter system.
Currently, there is a desire to add battery storage to solar plants. Battery storage allows for a number of features that enhance grid operation and enable higher penetration of solar power. However, known systems that incorporate battery storage in solar plants utilize separate inverters for the batteries and solar modules as sharing of DC power of the batteries and solar modules is not possible in a common inverter due to the mismatch of operating voltage between the batteries and solar modules. The use of separate inverters adds to the overall cost of the photovoltaic system and may affect system reliability.
It would therefore be desirable to provide a photovoltaic system capable of combining the DC power of the batteries and solar modules in the same inverter.